1. Field of the Application
The present application relates to an internal ferrule of a stator with blades as well as an annular stator of an axial turbomachine, in particular an internal ferrule of a diffuser with blade as well as a diffuser of an axial compressor. Such compressors are typically present in turbojets, turboprops and gas generators.
2. Description of Related Art
An axial compressor typically consists of a series of compression steps, of which each is composed of a circular arrangement of circumferential blades of which the bases are mounted on a rotor. A stator that serves as housing covers the rotor and the blades. The ends of the blades of the rotor move closely to the inside of the stator. Fluid, typically air, is thus moved and compressed along an annular track that is concentric relative to the axis of rotation of the rotor. The rotor thus consists of several rows of circumferential blades at some distance from one another. Rows of attached blades are mounted on the stator between the rows of rotor blades to direct the airflow between the two stages of the compressor. These diffuser blades typically possess an internal inner ferrule at their ends to delimit the primary flux at the lower level. This ferrule typically has an annular shape with an outer surface that is especially profiled to delimit the flux. The outer surface consists of a series of openings into which the ends of the blades fit, of which the base is attached to the stator. This ferrule also ensures “solidarity” among the blades at their ends if these are not free. The inside of the ferrule is covered with a material that is friable or more commonly called abradable. This abradable layer is able to work with one or more vanes on the rotor's circumference by friction to ensure a certain tightness. These vanes are more commonly called “lips” (of a labyrinth seal).
Depending on the dimensions and the used materials and also for reasons of ease of assembly, it may be of interest to segment the ferrule. Indeed, in the case of for example the realization of a ferrule made of a composite material, it may prove to be difficult to inject the resin of a composite material onto the long parts well enough, and hence, segmentation of the ferrule is interesting in view of reducing the length of the segments. Segmentation of the ferrule may also prove to be interesting to compensate for differential expansions at the blades themselves and the parts of the stator that supports the blades.
Document U.S. Pat. No. 4,395,195 discloses an internal ferrule of a compressor of a turbo-engine of which the ferrule is segmented into several sections. The orientation of the blades from the stator is variable so that the coupling between the blades and the ferrule is rotary. The joint between the different outer segments is accomplished between two neighboring blades by means of inner segments in the shape of a “C” of which the opening is directed toward the exterior and into which the outer segments of the ferrule fit (slider). Such a construction is fairly complicated and expensive. Moreover, assembly of the ferrule may prove to take long and therefore be expensive.
Document GB 727,608 discloses an internal ferrule of a stator for a gas turbine consisting of two segments. These two segments are linked with each other by making the end of one slide into the end of the other. These coupling means by means of sliding movement prevent all movement relative to the principal axis of the machine.
Relative to a mono-block ferrule, segmentation of the ferrule, however, has deteriorated aerodynamic properties as a possible disadvantage, notably at the level of the joint. Indeed, depending on the used materials, the precision of the realization and the assembly, the joint between two segments may present a certain projection or misalignment of the joint surfaces which delimits the primary flux.
Although great strides have been made in the area of axial compressors, many shortcomings remain.